From my own experience, with a properly performed high pull (and deadlifts/dead-squat if you do them) you will get enough stimulation to build a big, muscular and thick back. The only comment possible is to say that you will not build a "bodyduilding back" in which the lats need to be overdevelopped, it will be more of an athletic/strong looking back.
I sometimes add rows after high pulls. Properly performed ringh chin-ups or rows might also be done. 3-4 sets of 6-8 with a good peak contraction would be enough for most.
As back exercises go, I could happily just perform high pulls and deadlifts. How would you execute a straight bar deadlift to maximise back development? Do you concentrate strongly on bringing the bar to the hip crease after the knees?
Also, How would you intergrate straight bar deadlifts into a program involving 2 pulling days? I am currently following your 3,3,3,6,6,6 program with 2 push days, 2 pulls days and 1 leg day. Is it possible to deadlift on both days if say one was strength dedicated and one was speed dedicated?
The best form of deadlift to build the upper back is a snatch-grip deadlift from pins (2" below knees), sweeping in the bar toward the hip crease. In fact I used that movement yesterday with an IFBB pro bodybuilder.
With the 3,3,3,6,6,6 scheme it is possible to do both deadlifts and high pulls on both days, especially that form of deadlift which is easier on the nervous system.
Baring in mind the volume of deadlifting. would it be wise to replace the strength capacity section of the workout for a 3rd movement (rows) for 4 x 6/8 or would you just use different exercises for the strength capacity section?
On the lower intensity day would u ever consider performing deadlift-shrugs with 1 deadlift and 3 shrugs at the top to ensure the upper back is still being challenged whilst the lower back isn't. I think john meadows advocates these to his bodybuilders.
So im high pulling as per the 10 day cycle posted on your 3 zones of intensity note. I would like to add more high pull volume is this ok? I was thinking about adding clusters or something for day 3 (day 1 of high pulls). What would you do?